Typically, there are many voltages such as comparator trip points and transistor threshold voltages associated with an integrated circuit which are not readily accessible. Such voltage measurements cannot easily be made if the integrated circuit has been packaged. Further, when such voltage measurements are made, the accuracy is detrimentally affected by loading effects resulting from capacitance associated with an external measurement. A common way to test the operability of an integrated circuit is to measure transistor threshold voltages. Unfortunately, process variations which are inherent in the fabrication of integrated circuits may greatly vary the threshold voltage of a transistor and drastically affect the operability of the circuit, especially if the circuit is an analog circuit. A transistor having a small threshold voltage typically exhibits excessive source electrode to drain electrode current leakage at high temperatures. Further, a transistor having a large threshold voltage is also a cause of problems. For example, in integrated circuits utilizing capacitors and conventional transmission gates, charging problems exist as a result of large "on" impedances associated with transmission gates having transistors with large threshold voltages. Threshold voltages may vary not only with different silicon but may also vary across a single silicon wafer. It is of course desirable to detect integrated circuits which will fail at temperature extremes at a test probe stage at room temperature rather than after hours of temperature cycling in expensive test equipment. Process control measurement of threshold voltages may be made manually. However, resulting data may be very inaccurate since only a few random samples of silicon wafers may be practically measured manually from a cost effective standpoint. Further, due to the impracticality of a thorough test probing of multiple silicon wafers by an individual, data is typically only obtained from a small sample of devices in only a portion of a silicon wafer. As a result, the presence and amount of threshold voltage variation across a silicon wafer, particularly around the edges, is usually not known.